Electrical control system

ABSTRACT

A feedback control system for controlling the acceleration and/or deceleration curve of an automatic material handling apparatus, as for example, an automatic or semi-automatic robot used in conjunction with delivering and retreiving material from a storage warehouse, wherein the distance from a fixed or variably selectable point is sensed and utilized to generate a speed curve for controlling the incremental variation in speed of the material handling device up to a preselected maximum speed or down to zero speed.

United States Patent Cassel Mar. 26, 1974 ELECTRICAL CONTROL SYSTEM 3.504.362 3/1970 Feldmann 246/!87 B [75] Inventor: Har ison H. Cassel, Royal Oak 3,334,224 8/1967 Allen et al 246/182 B Mich.

Primary Examiner-Gerald M. Forlenza [73] Asslgnee gi g Company Detrolt Assistant ExaminerGeorge H. Libman 1c Attorney, Agent, or Firm--Harness, Dickey & Pierce [22] Filed: Jan. 26, 1972 t A l t D t ed U 5 pp [ca a a A feedback control system for controlling the acceler- [63] f of July 1969 ation and/0r deceleration curve of an automatic matea an one rial handling apparatus, as for example, an automatic or semi-automatic robot used in conjunction with de- 104/1 1 4 g g 3 g livering and retreiving material from a storage ware- [58] i 4 246/183 B C house, wherein the distance from a fixed or variably 318/604 104/1 selectable point is sensed and utilized to generate a speed curve for controlling the incremental variation [56] References Cited in speed of the material handling device up to a prese- UNITED STATES PATENTS lected maximum speed or down to zero speed.

3,524,005 8/1970 Smith 246/182 B 23 Claims, 21 Drawing Figures 5 6?! A? Mia? .f/f/f'l/W/fll 2%1'2W1 77/ i/VV/I'l/ 47/ fa /7724?! A? W Jam/4X /7 PATENIEBIAR 26 I874 sum 02 0F 18 WWW/ m PATENTEDIIARZB I874 saw us or 18 INVENTOR.

sum 060F13 PATENTEDIAR26 m4 PAIENIEDmzGmn sum 13 0F 18 INVENTOR. z drr/jaw X46255? 1 ELECTRICAL CONTROL SYSTEM Attention is directed to Assignees copending application of Ralph R. Griner, Ser. No. 838,767, filed July 3, 1969 for Analog Control System now US. Pat. No. 3,638,575.

BACKGROUND AND SUMMARY OF THE DEVELOPMENT This invention relates generally to an acceleration and/or deceleration, feedback, control system for a driving motor, and more particularly to an acceleration and/or deceleration characteristic control system which is particularly adapted to be utilized in conjunction with an automatic or semi-automatic material handling device or system, the acceleration or deceleration curve being generated in accordance with a speed versus distance function.

In material handling systems which incorporate a conveying device, as for example, a robot for handling palletized loads, it is desirable to operate the material handling device at as great a speed as is practical to get from one station to a position adjacent another station and then to decelerate the material handling device as rapidly as possible consistent with accurately positioning the material handling device at the preselected stopping point. Also, it is necessary to prevent undue horizontal forces on the material being handled.

Automated material handling machines are in common use in many processing industries, as for example, in the automatic warehousing industries. These machines are particularly adapted to automatically transfer palletized loads from an input station to a preselected address station which corresponds to a particular bay within the storage complex. Further, the automatic transfer system must elevate the palletized load to a preselected level within the bay and deposit the load at that level. Subsequently, the automatic transfer mechanism may be given a command to pick up a second load at a different station. and deliver the second load to a conveying apparatus for pickup. Thus, the automatic transfer mechanism must accelerate to a speed consistent with the capability of being able to decelerate and accurately stop at the second pickup address. Thereafter, the transfer mechanism will accelerate toward the home station and finally follow a deceleration cycle to stop at the home station and deposit the load.

The system of the present invention is described in conjunction with an automatic robot type of material handling which is adapted to be utilized in an automatic warehousing complex. However, it is to be understood that other material handling systems may utilize the principles of the present invention, as for example, systems which are adapted to transfer workpieces through a successive number of processing stations. In certain areas of the material handling control art, systems have been utilized to control acceleration and deceleration (dv/dt) using a feedback signal from a tachometer, of the speed sensing type, to control the system. Thus, the system is controlled in response to a speed versus time relationship. Certain other systems have been evolved which utilize a relatively complex hydraulic motor control system which must be very precisely controlled to overcome or anticipate the inherent mechanical" and hydraulic inertia of the system. Thus, it is neccessary to predict the response time of the various elements of the system, for example, the hydraulic portion of the system, in order to accurately position the work handling assemblyrelative to the final position desired.

In accordance with the system of the present invention, an electric analog feedback control has been devised which utilizes the principle of controlling the speed of a material handling apparatus in response to a speed versus distance relationship. Specifically, a continuously operating pulse generating encoder assembly, such as a Baldwin precision shaft positioning encoder, may be utilized to generate output pulses in direct response and directly driven by the drive wheels or other position responsive portion of the material handling apparatus. The continuously generated pulses are not utilized during the full speed operation of the system. However, when it is decided to accelerate or decelerate along a preselected curve, a pickup device for the encoder is energized. The energization can be accomplished practically instantaneously, and the sensed pulses are utilized as a measure of distance traveled and a control signal is generated in response to the counting of the pulses or conversion of the pulses to an analog signal to control the speed of the material handling apparatus.

The output from the pickoff once energized, appears as a series of pulses, the number of pulses being a fixed constant per linear distance of travel of the material handling assembly. These pulses are fed into a counter and digital to analog converter system, the output of which varies in accordance with a preselected function of the number of input pulses. This output is amplified through an amplifying system and is fed to a control for the motor which is driving the particular handling assembly being controlled. In the case of the illustrated example, the output of the amplifier may be utilized to control the conduction of a silicon controlled rectifier type of electric motor control or may be utilized to energize the control winding of a saturable reactor type of motor control system.

Automatic systems of the type referred to generally comprise a carrier or automatic robot which is movable along the trackway, the trackway being disposed adjacent to and parallel with the open side of a storage frame. The storage frames define storage racks or bins in which palletized material loads are stored. A carriage is mounted on the carrier for vertical movement, the carriage being provided with a work handling platform or a pair of forks for transferring a load laterally between the carriage and the storage frame at selected ones of the racks or bins. The carrier may be disposed in an aisle between two storage frames with a platform or a pair of forks being insertable into either storage frame either by turning of the carriage or by symmetrical movement of the platform in either lateral direction.

The carrier preferably has a home position or input station which may, for example, be located at one end of the aisle. The input station is conveniently located forloading and unloading the carrier and preferably serves as a data input point from which the carrier, carriage and platform or forks, start in a sequence of movement designed to deposit a load in a storage frame, retrieve a load from a storage frame or transfer loads within the system in accordance with the data received at the input point. The system could further be expanded to perform any other series of movements required to the operation of a material storage system. 

1. In a material handling apparatus for delivering material from one station to another including a robot type material carrier and a motor for driving the carrier, the improvement comprising a control system for controlling the acceleration and/or deceleration of the carrier to an ultimate desired speed comprising signal generating means for continuously generating a digital signal formed of a series of successive pulses, each pulse being representative of distance travelled during at least a selected period of time, controlled conducting means transmitting said digital signal during a portion of said at least a selected period of time, and function generator means for generating a speed versus distance acceleration and/or deceleration continuous curve in response to said transmitted signal for controlling the operation of the motor in response to a characteristic of said curve, said speed versus distance curve being a function of the distance the carrier is at a particular instant from the point at which the ultimate desired speed is to be achieved.
 2. The improvement of claim 1 wherein the motion of the carrier is a linear horizontal motion.
 3. The improvement of claim 2 wherein said digital signal is generated during a period of time when the carrier is moving.
 4. The improvement of claim 2 wherein said speed versus distance curve which is an analog signal representing a function of the number of input digital pulses.
 5. The improvement of claim 1 wherein said material handling apparatus is an automatic warehousing system which is capable of automatically accelerating or decelerating upon the sensing of a preselected position relative to the storage racks of the warehouse and the carrier is a robot which may be automatically controlled during certain portions of its cycle, the improvement further comprising pulse generating means directly driven in response to travel of the wheels of the robot, said pulse generator being capable, if enabled, of delivering digital pulses, the number of the digital pulses bearing a direct linear relationship with the distance traveled by the robot.
 6. The system of claim 5 wherein said digital pulses represent as increments of position of the robot relative to the warehousing assembly.
 7. The system of claim 6 wherein said function generator means includes a digital to analog convertor for converting the digital pulse signals to an analog signal, the function generator also including means for varying the analog signal as a function of the transmitted pulses.
 8. The improvement of claim 7 wherein said analog function signal is utilized to control the motor driving the carrier in response to the amplitude of the analog signal.
 9. The improvement of claim 8 wherein said controlled conducting means includes gate means for transmitting the digital pulses in response to sensing a particular position of the robot relative to the warehousing system.
 10. The system of claim 9 wherein said gate means, in response to sensing a preselected position, initiates the start of a deceleration cycle, at least a portion of which includes decelerating of the motor along said deceleration curve.
 11. The improvement of claim 10 wherein said digital and analog signal are electrical signals and said gating means is an electrical gate for transmitting the signals.
 12. The system of claim 11 wherein said portion of said at least selected period of time is commenced upon sensing the preselected position relative to a selected bay of the warehousing system and is terminated in response to stopping of the robot.
 13. The improvement of claim 11 wherein said portion is initiated upon the start of the acceleration of said robot and is terminated upon the achievement of a preselected maximum speed.
 14. In a material handling apparatus for delivering material from one station to another including a robot type material carrier and a motor for driving the carrier to An ultimate desired speed, the method of controlling the acceleration and/or deceleration of the carrier comprising continuously generating a digital signal formed of a series of successive pulses, each pulse being representative of distance travelled during at least a selected period of time, transmitting said digital signal during a portion of said at least a selected period of time, and generating a speed versus distance acceleration and/or deceleration continuous curve in response to said transmitted signal for controlling the operation of the motor in response to a characteristic of said curve, said speed versus distance curve being a function of the distance the carrier is at a particular instant from the point at which the ultimate desired speed is to be achieved.
 15. The method of claim 14 wherein the motion of the carrier is a linear horizontal motion.
 16. The method of claim 15 wherein said digital signal is generated during a period of time when the carrier is moving.
 17. The method of claim 15 further including generating a speed versus distance curve which is an analog signal representing a function of the number of input digital pulses.
 18. The method of claim 14 wherein said material handling apparatus is an automatic warehousing system which is capable of automatically accelerating or decelerating upon the sensing of a preselected position relative to the storage racks of the warehouse and the carrier is a robot which may be automatically controlled during certain portions of its cycle, the method further comprising directly driving the pulse generator in response to travel of the wheels of the robot and generating digital pulses; the number of the digital pulses being a direct linear relationship with the distance traveled by the robot.
 19. The method of claim 18 wherein said digital pulses are represented as increments of position of the robot relative to the warehousing assembly.
 20. The method of claim 19 further including converting the digital pulse signals to an analog signal, the function generator also varying the analog signal as a function of the transmitted pulses.
 21. The method of claim 20 further including utilizing the function signal to control the motor driving the carrier in response to the amplitude of the analog signal.
 22. The method of claim 21 further including initiating the start of a deceleration cycle in response to sensing a preselected position, at least a portion of which includes deceleration of the motors along said deceleration curve.
 23. The method of claim 22 further including commencing said at least selected period of time upon sensing the preselected position relative to the warehousing system and terminated the period in response to stopping of the robot. 